U.S. Pat. No. 6,079,821 issued to Chwalek et al. discloses a continuous ink jet printhead in which deflection of selected droplets is accomplished by asymmetric heating of the jet exiting the orifice.
U.S. Pat. No. 6,554,410 by Jeanmaire et al. teaches an improved method of deflecting the selected droplets. This method involves breaking up each jet into small and large drops and creating an air or gas cross flow relative to the direction of the flight of the drops that causes the small drops to deflect into a gutter or ink catcher while the large ones bypass it and land on the medium to write the desired image or the reverse, that is, the large drops are caught by the gutter and the small ones reach the medium.
U.S. Pat. No. 6,450,619 to Anagnostopoulos et al. discloses a method of fabricating nozzle plates, using CMOS and MEMS technologies which can be used in the above printhead. Further, in U.S. Pat. No. 6,663,221, issued to Anagnostopoulos et al, methods are disclosed of fabricating page wide nozzle plates, whereby page wide means nozzle plates that are about 4″ long and longer. A nozzle plate, as defined here, consists of an array of nozzles and each nozzle has an exit orifice around which, and in close proximity, is a heater. Logic circuits addressing each heater and drivers to provide current to the heater may be located on the same substrate as the heater or may be external to it.
For a complete continuous ink jet printhead, besides the nozzle plate and its associated electronics, a means to deflect the selected droplets is required, an ink gutter or catcher to collect some of the droplets, an ink recirculation or disposal system, various air and ink filters, ink and air supply means and other mounting and aligning hardware are also needed.
In these known continuous ink jet printheads, the nozzles in the nozzle plates are arranged in a straight line and for robust operation and manufacturability, they are spaced at most as close as about 42.33 microns apart, which corresponds to about 600 nozzles per inch. Drop volumes produced by these nozzle arrays depend on the diameter of the exit orifice of the nozzles and the velocity of the jet. Typical volumes range from a few picoliters to many tens of picoliters.
As already mentioned, all continuous ink jet printheads, including those that depend on electrostatic deflection of the selected droplets (see for example U.S. Pat. No. 5,475,409 issued to Simon et al), an ink gutter or catcher is needed to collect the unselected droplets. Such a gutter has to be carefully aligned relative to the nozzle array since the angular separation between the selected and unselected droplets is, typically, only a few degrees. The alignment process is typically a very laborious procedure and increases substantially the cost of the printhead. The printhead cost is also increased because each gutter must be aligned to its corresponding nozzle plate individually and one at a time.
The gutter or catcher may contain a knife-edge or some other type of edge to collect the unselected droplets, and that edge has to be straight to within a few tens of microns from one end to the other. Gutters are typically made of materials that are different from the nozzle plate and as such they have different thermal coefficients of expansion so that if the ambient temperature changes the gutter and nozzle array can be in enough misalignment to cause the printhead to fail. Since the gutter is typically attached to some frame using alignment screws, the alignment can be lost if the printhead assembly is subjected to shock as can happen during shipment. If the gutter is attached to the frame using an adhesive, misalignment can occur during the curing of the glue as it hardens, resulting in yield loss of printheads during their assembly.
The US publication 2006/0197810 A1-Anagnostopoulos et al. discloses an integral printhead member containing a row of inkjet orifices.
There's a need to accurately print with inkjet streams closer together widthwise on paper than is presently possible. Rows of inkjet's are limited in how close they can be together by the necessity for separation between ink droplets from adjacent orifices. The spacing between rows of inkjets in the machine direction is limited by the large space mounting requirements for a second row of inkjets. Therefore, a second row of 600 nozzles per inch inkjets cannot be arranged to overlap earlier printed material at 600 nozzles per inch in alignment, as the paper is not stable enough after wetting by the first inkjet in the first row to align, within 20 micrometers, with a second row of jets. Accurate alignment with the pattern from the first row after the distance of several centimeters the paper has traveled to the second row of nozzles is not possible. Further aligning the jets themselves is difficult to achieve and to maintain. If a second row of nozzles could be aligned to print between the ink from the nozzles of the first row a greater density of nozzles per width inch on paper could be achieved.
There is a need for a method of providing ink streams from more nozzles per inch in a widthwise direction to paper beneath the ink streams than has heretofore been possible without alignment problems and without the need to utilize very small droplets of ink. There is a need for an arrangement where a second row of nozzles is aligned to a first printhead and maintains this alignment during operation and is so close to the first printhead that paper stretching is not in issue